There are numerous instances micro-robots, many of which require powered external infrastructure such as large electromagnets, surfaces with local magnetic fields, capacitive electrode surfaces) or similar provisions. Even with the powered external infrastructure, they can apply only minute interaction forces with their environments. In contrast, insects such as weaver ants have no required infrastructure yet can exert substantial forces when normalized to bodyweight.
At small scales, insects exploit interaction forces like adhesion that, unlike coulomb friction, scale with area and do not depend on the magnitude of a normal force. There are many examples of insects that use adhesive pads, scopulae, and other microscopic features to attach to surfaces; with these features, insects can apply interaction forces many times their body weight.
However, adhesion without a method of release is not useful; an insect or robot would become stuck and could not move. This problem has been reported for both small robots and moving MEMS devices. In addition, at smaller scales, legged locomotion requires higher step rates than at larger scales to maintain the same absolute velocity. Therefore, adhesives must engage and disengage more quickly at small scales. To allow easy and fast release of adhesion, an insect or microrobot needs a controllable adhesive that can be activated for applying large interaction forces when required, and deactivated for locomotion with low energy expenditure. Indeed, most insects that use various forms of adhesive pads have controllable adhesion.
What is needed is a method of enabling small robots to move easily and apply interaction forces that are orders of magnitude larger than their weights using controllable dry adhesive that function on a variety of smooth surfaces and allow both large force generation and high step rates.